At night on a tight site, two all-terrain cranes pick, turn, and place a 221-ft. bridge in under an hour.

Imperial Crane Services Inc., Bridgeview, Ill., had to work quickly in the middle of the night when two of its cranes picked, rotated, and placed a new 221-ft. pedestrian bridge over railway tracks in Lake Forest, Ill. The new steel bridge connects the Middlefork Savanna Forest Preserve with Lake Forest Academy and Townline Community Park. It is part of a larger overall project that will connect trails and nature areas in the region. It is also part of the city’s master bicycle plan.

The new span replaces a bridge of decorative stone, which had been removed years before. That historic stone bridge was once part of the driveway for the estate of Jonathan Ogden Armour, head of the Armour meat-packing company.

When the historic old bridge was removed, its abutments were saved. The new steel pedestrian bridge was set within them.

Tight Site and Schedule

The project’s general contractor was Copenhaver Construction, Gilberts, Ill. The site was tight and challenging, with little space on either side of the two Metra railroad tracks, and mature trees on the hills on both sides. The west side of the tracks, in particular, offered little room between the railway and the trees.

Copenhaver selected Imperial Crane Services to provide the lifting services needed to assemble and set the new bridge.

After analyzing the lifting requirements, Imperial decided to use two of its all-terrain cranes: a 550-ton-capacity Grove GMK7550 and a 330-ton-capacity Liebherr LTM 1300-6.2.

“We chose these two rigs because they provided the reach and capacity we needed while working in the space available,” said Imperial Crane vice president Jay Mooncotch. “We needed their capacity to give us a margin of safety while lifting the 110-ton bridge at the required radii.”

The bridge was delivered to the site in five sections, which were lined up parallel to the easternmost rail line and then assembled into the bridge’s full 221-ft. length.

The plan called for the fully-assembled, 14′ x 14′ x 221′, bridge to be lifted by both cranes, swung 90°, lined up, and set over the existing abutments. Because the work could not interfere with Metra train service, the bridge had to be picked and set between times that Metra trains rumbled through the construction site.

The longest gap between trains, about an hour, came between 1:30 and 2:30 a.m., so that’s when the lift was scheduled to take place. Mooncotch said the company used three-dimensional lift-planning software and “lots of field measuring and layout” to engineer the late-night lift. He added that since the site was tight and the bridge was long, putting the cranes in the right locations was vital. “During maneuvering, the bridge would clear each crane boom by a couple of feet,” he said.

Midnight Tango

Imperial positioned the Grove GMK7550 just west of the tracks, set its outriggers at full width, extended its five-section boom to 150 ft., and reeved its load block with four parts of line. The crane then reached high and across the tracks, where the load block was rigged to a spreader beam that was connected near one end of the bridge. Operator Glenn Marvin was at the controls.

Imperial’s Liebherr LTM 1300-6.2 was set up on the east side of the tracks and about 100 ft. north of the Grove. Its outriggers were set to full width, its five-section boom telescoped out to 150 ft., and its load block reeved with four parts of line. The Liebherr’s block was connected to a spreader beam that was connected near the end of the bridge opposite from the one supported by the Grove. Mike Swiderski Jr. was operating.

With everything rigged and ready, the one-hour working window started as soon as a Metra train raced by at about 1:30 a.m.

In what one impressed local official called “a dance of cranes,” the GMK7550 and LTM 1300-6.2 worked in unison to lift and maneuver the bridge back and forth while turning it 90° before setting it over the existing abutments in time for the next Metra train to zip beneath it about 2:30 a.m. The back-and-forth maneuvering was needed to work the boom between the cranes as it was turned. The operators and signalpersons were all connected by radio to provide instant and accurate communication, said Mooncotch.

The bridge weighed about 220,000 lbs. with rigging. During the lift, the Grove GMK7550 carried about 50% of the weight and worked at radii to
80 ft., while the Liebherr LTM 1300-6.2 also handled about 50% of the weight and worked at radii to 60 ft. Both cranes needed hook heights of about 80 ft. for the bridge to clear trees and the existing abutments.

Said Mooncotch, “The fixed working time, close crane coordination, and nighttime conditions made this a really challenging lift. It’s a testament to the cranes’ capacity and control, our operators’ skill, and our pre-lift planning that it went so smoothly and precisely.”